Introduce yml config validator script

[bsmid]

This script would check yml configs statically (no need for agent or the source of metrics to run).
Some of the checks we can do:

• general yaml validation and whether format conforms to Agent yaml format
• check whether labels are present, warn if description is missing
• check lowercase/uppercase in labels, descriptions...
• check units that were used (compare to list of standard units present in Agent configs)
• any other check that might be useful